Omnitarg (chemical name: pertuzumab) is an experimental targeted therapy medicine. Doctors have been studying how Omnitarg could be used to treat several types of cancer, including metastatic HER2-positive breast cancer. Metastatic breast cancer is cancer that has spread to parts of the body away from the breast, such as the bones or liver.

The CLEOPATRA (CLinical Evaluation Of Pertuzumab And TRAstuzumab) study has shown that women diagnosed with metastatic HER-2 positive breast cancer who were treated with a combination of Omnitarg, Herceptin (chemical name: trastuzumab), and Taxotere (chemical name: docetaxel) lived 6 months longer without the cancer growing (progression-free survival) compared to women treated with only Herceptin and Taxotere.

The results were presented at the 2011 San Antonio Breast Cancer Symposium and published online in the New England Journal of Medicine.

HER2-positive breast cancers have too many copies of the HER2/neu gene, which makes too much of the HER2 protein. HER2-positive breast cancers tend to be more aggressive than cancers that are HER2-negative. Both Herceptin and Omnitarg work against HER2-positive breast cancers by blocking the cancer cells' ability to receive growth signals. Both medicines are given intravenously.

Herceptin, also a targeted therapy, is already approved by the U.S. Food and Drug Administration (FDA) to treat advanced-stage, HER2-positive breast cancer and to lower the risk of recurrence (the cancer coming back) of early-stage, HER2-positive breast cancer with a high risk of recurrence.

Omnitarg currently is not approved by the FDA to treat breast cancer. Lab research suggests that Omnitarg can improve Herceptin's ability to weaken or destroy HER2-positive breast cancers. So doctors have been studying how these two medicines could be used together to treat HER2-positive breast cancer. Doctors sometimes refer to the Herceptin and Omnitarg combination as dual HER2 antibody therapy.

In the CLEOPATRA study, 808 women diagnosed with HER2-positive metastatic breast cancer that hadn't been treated yet were randomly assigned to receive one of two treatment regimens:

half the women got Herceptin, Taxotere, and Omnitarg

half the women got Herceptin, Taxotere, and a placebo infusion (instead of Omnitarg)

More than 80% of the women who got Herceptin, Taxotere, and Omnitarg had some response to the treatment (called objective response rate) compared to 69.3% of the women who got only Herceptin and Taxotere.

Progression free-survival was 6 months longer for women treated with Herceptin, Taxotere, and Omnitarg compared to women treated only with Herceptin and Taxotere (18.5 months compared to 12.4 months). Half of all the women treated with Herceptin, Taxotere, and Omnitarg lived without the cancer growing for more than 18.5 months and half lived with no cancer growth for shorter periods of time. Half of all the women treated with only Herceptin and Taxotere lived without the cancer growing for more than 12.4 months and half lived with no cancer growth for shorter periods of time.

The researchers need to follow the women for more time to see if overall survival -- the time a woman lives with or without the cancer growing -- is better when Omnitarg is added to Herceptin and Taxotere. Still, when these results were presented, 17% of the women who got Omnitarg had died compared to 24% of the women who didn't get Omnitarg.

There was only a small increase in side effects in women treated with Herceptin, Taxotere, and Omnitarg compared to women treated only with Herceptin and Taxotere.

The most common serious side effects in both treatment groups were low white blood cell counts (called neutropenia), with or without fever, and severe diarrhea. Problems with heart function or developing heart failure can sometimes be side effects of Herceptin. The CLEOPATRA study found that adding Omnitarg didn't increase the risk of heart problems.

If you're being treated for metastatic HER2-positive breast cancer, you and your doctor may be considering a number of treatment options. If you're willing to participate in a clinical trial, you may have even more options, possibly including an experimental treatment such as Omnitarg. Talk to your doctor about clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages for more information.

Stay tuned to Breastcancer.org Research News for updates on the CLEOPATRA study.